In a small bowl, combine the flour, sugar, baking powder, salt and cinnamon. In another bowl, whisk the eggs, milk, butter and vanilla. Stir into dry ingredients just until moistened.
Transfer to eight 4-1/2-in. x 2-1/2-in. x 1-1/2-in. loaf pans coated with cooking spray. Bake at 325° for 18-22 minutes or until golden brown. Immediately remove from pans to a wire rack to cool completely.
In a microwave, melt chocolate chips and butter. Add milk; stir until smooth. Dip tops of doughnuts in glaze. Return to wire rack; let stand until set.